StackOverflow2013

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POCan I force the compiler to optimize a specific method?
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copied!<p>Is there an attribute I can use to tell the compiler that a method must always be optimized, even if the global <code>/o+</code> compiler switch is not set?</p> <p>The reason I ask is because I'm toying with the idea of dynamically creating a method based on the IL code of an existing method; the manipulation I want to do is reasonably easy when the code is optimized, but becomes significantly harder in non-optimized code, because of the extra instructions generated by the compiler.</p> <hr> <p>EDIT: more details about the non-optimizations that bother me...</p> <p>Let's consider the following implementation of the factorial function:</p> <pre><code>static long FactorialRec(int n, long acc) { if (n == 0) return acc; return FactorialRec(n - 1, acc * n); } </code></pre> <p><em>(Note: I know there are better ways to compute the factorial, this is just an example)</em></p> <p>The IL generated with optimizations enabled is quite straightforward:</p> <pre><code>IL_0000: ldarg.0 IL_0001: brtrue.s IL_0005 IL_0003: ldarg.1 IL_0004: ret IL_0005: ldarg.0 IL_0006: ldc.i4.1 IL_0007: sub IL_0008: ldarg.1 IL_0009: ldarg.0 IL_000A: conv.i8 IL_000B: mul IL_000C: call UserQuery.FactorialRec IL_0011: ret </code></pre> <p>But the unoptimized version is quite different</p> <pre><code>IL_0000: nop IL_0001: ldarg.0 IL_0002: ldc.i4.0 IL_0003: ceq IL_0005: ldc.i4.0 IL_0006: ceq IL_0008: stloc.1 IL_0009: ldloc.1 IL_000A: brtrue.s IL_0010 IL_000C: ldarg.1 IL_000D: stloc.0 IL_000E: br.s IL_001F IL_0010: ldarg.0 IL_0011: ldc.i4.1 IL_0012: sub IL_0013: ldarg.1 IL_0014: ldarg.0 IL_0015: conv.i8 IL_0016: mul IL_0017: call UserQuery.FactorialRec IL_001C: stloc.0 IL_001D: br.s IL_001F IL_001F: ldloc.0 IL_0020: ret </code></pre> <p>It is designed to have only one exit point, at the end. The value to return is stored in a local variable.</p> <p>Why is this an issue? I want to dynamically generate a method that includes tail call optimization. The optimized method can easily be modified by adding the <code>tail.</code> prefix before the recursive call, since there nothing after the call except <code>ret</code>. But with the unoptimized version, I'm not so sure... the result of the recursive call is stored in a local variable, then there's a useless branch that just jumps to the next instruction, the the local variable is loaded and returned. So I have no easy way of checking that the recursive call really is the last instruction, so I can't be sure that tail call optimization can be applied.</p>

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